The present invention relates to a multiplexing apparatus which multiplexes data items received from lines on plural terminal sides to transmit the multiplexed data onto a line on a network side, and demultiplexes the multiplexed data received from the line on the network side to transmit the demultiplexed data items onto the lines on the plural terminal sides.
A constitution of a conventional multiplexing apparatus is shown in FIG. 5.
In FIG. 5, reference numerals 21 to 23 denote terminal interface units. Here, the terminal interface unit 21 is a voice line interface unit which accommodates a PBX (Private Branch Exchange) 5 accommodating voice terminals such as a telephone 6. The terminal interface unit 22 is a data line interface unit for accommodating a data terminal 4. The terminal interface unit 23 is an FR (Frame Relay) line interface unit for accommodating an FR terminal 3. Furthermore, reference numeral 24 denotes a network interface unit for accommodating a line on a network 1 side.
The terminal interface units 21 to 23 and the network interface unit 24 are connected to each other by an internal bus 26, and data is sent/received therebetween via the internal bus 26. Furthermore, reference numeral 25 denotes an internal bus control unit which arbitrates the bus right among devices connected to the internal bus 26.
In the terminal interface units 21 to 23, data transmitted from the terminal is received by the terminal-side line interface sub-unit 211, and then converted to a data block (hereinafter generically called packet type data) as a certain unit, to which a destination is given, by an assembly/disassembly sub-unit 28. The data block is an ATM cell, an IP packet and the like, and determined by a protocol adopted in the network 1. The data block is transmitted to the internal bus 26 from an internal bus interface sub-unit 271. Furthermore, in the terminal interface units 21 to 23, packet type data transmitted from the network interface unit 24 via the internal bus 26 is received by the internal bus interface sub-unit 271 and then disassembled by the assembly/disassembly sub-unit 28, and data is extracted. The extracted data is transmitted from the terminal-side line interface sub-unit 211 to the terminal.
On the other hand, in the network interface unit 24, the packet type data transmitted from each of the terminal interface units 21 to 23 via the internal bus 26 is received by an internal bus interface sub-unit 272, and then sent to a priority control sub-unit 242 via a network synchronizing sub-unit 241. The packet type data is once stored in a priority control buffer 243. Thereafter, packet type data is sequentially synchronized with the line on the network 1 side in the order of descending priorities, the priority being stored in a header of the packet type data, by the network synchronizing sub-unit 241 to be transmitted to the line on the network 1 side. Furthermore, in the network interface unit 24, the packet type data transmitted from the line on the network 1 side is received by the network synchronization sub-unit 241, and then transmitted from the internal bus interface sub-unit 272 to the internal bus 26 to be received by each of the terminal interface units 21 to 23 as described above.
Furthermore, in the network interface unit 24, a clock extraction sub-unit 244 extracts a network clock synchronized with the line on the network 1 side, and sends the extracted network clock to the internal bus control unit 25. From this network clock, a clock generation sub-unit 251 of the internal bus control unit 25 generates operation clocks for the internal bus 26 and the terminal interface units 21 to 23, and distributes the operation clocks to the internal bus 26 and the terminal interface units 21 to 23.